There have been active studies and development of light emitting devices having semiconductor light emitting elements and phosphors, which are gaining attention as the next-generation light emitting devices expected to achieve lower power consumption, reduction of size, high intensity, and further a wide range of color reproducibility. The primary light emitted by a semiconductor light emitting element typically has a peak emission wavelength in the near-ultraviolet region to the blue region, having the peak emission wavelength in a wavelength range from 380 nm to 480 nm inclusive, for example. Light emitting devices using various kinds of phosphor tailored for specific applications have been proposed as well.
A variety of light emitting devices for use as lighting devices have been also developed, with various approaches to improving the output performance of such light emitting devices under study. For enhancement of the output performance of a light emitting device, a phosphor having a major emission peak in the yellow region, which has high luminous efficacy and represents the complementary color of blue, is typically employed. For a light emitting device that can be used for generic lighting fixtures, having high color rendering properties (the term “having high color rendering properties” essentially means having an average color rendering index Ra of 80 or higher) is also an important feature in addition to improvement of its output performance.
The average color rendering index Ra is a metric generally used as an indicator of color rendering properties based on assessment of whether test colors (R1 to R8) look natural or not. For light emitting devices useable as generic lighting fixtures, making the test colors look natural is important: increasing the average color rendering index Ra is an important consideration. In the case of a lighting fixture using a light emitting diode (LED) light source, however, light emitted by an LED light source has notably high emission peaks in the blue and yellow regions compared to a traditional light source such as a high intensity discharge lamp. As a result, the color of an illuminated object can look dull even when the light source has a high average color rendering index Ra. This is because yellow is generally a hue indicative of fading of color and thus makes the illuminated object look as if faded.
In the fashion industry, for example, light emitting devices that make illuminated objects look yellowish are tend to be avoided because they impair the clearness of illuminated objects. For such light emitting devices that are used in sales of articles and the like, a premium is often placed on how the illuminated object looks in addition to the demand for merely ensuring brightness.
To meet this demand, an LED lamp having an LED light source and a filter is described in International Publication No. 2011/108203 Pamphlet (PTL 1), for instance. The LED light source described in PTL 1 includes a blue LED having a major emission peak in a wavelength region from 440 nm to 460 nm, a green or yellow phosphor to be excited by the light emitted by the blue LED, and a red phosphor to be excited by the light emitted by at least one of the blue LED and the green or yellow phosphor. The filter described in PTL 1 reduces the spectral radiant intensity in at least part of a wavelength region from 570 nm to 590 nm of the light emitted by the LED light source. PTL 1 describes that use of the filter for reducing the spectral radiant intensity in a specific wavelength region and inclusion of a red phosphor in the LED light source can make not only medium saturated colors (according to PTL 1, the medium saturated colors are defined as the test colors with medium saturation, R1 to R8) but a clear red color look natural. The LED lamp described in PTL 1 includes a filter, however, which adds to operations in the manufacturing process of the LED lamp and hence increases its manufacturing costs. Additionally, because the filter decreases the spectral radiant intensity in at least part of the wavelength region from 570 nm to 590 nm, it causes reduction in power efficiency of the lighting device.
International Publication No. 2012/104937 Pamphlet (PTL 2) describes a high-saturation LED module capable of improving the clearness of the color of an illuminated object even when the ambient light has a high correlated color temperature and consequently reproducing the color favorably. According to descriptions in PTL 2, a correlated color temperature is from 4600 K to 7200 K inclusive and a distance from perfect radiator locus on uv-ordinates (duv) is from −12 to −6 inclusive. As a result of duv being from −12 to −6 inclusive, the reddish component relatively increases, which can enhance the color reproducibility, particularly the color reproducibility in the red region. However, large deviation of the chromaticity range from the blackbody locus increases the reddishness of the color of the emitted light itself, which in turn can make an illuminated object look reddish.
International Publication No. 2013/150470 Pamphlet (PTL 3) describes that “crisp white” can be provided by use of a light emitting element that emits light in the near-ultraviolet region and a light emitting element that emits light in the blue region. Incorporation of a light emitting element that emits light in the near-ultraviolet region however causes no change in the emission peak in the yellow region, leaving the inherent possibility of an illuminated object looking yellowish.